An electrophotographic light-sensitive material usually comprises an electrically conductive support and a light-sensitive layer on the support. The light-sensitive layer is provided by coating a mixture of inorganic photoconductor e.g., zinc oxide, titanium oxide, cadmium sulfide, selenium, and an alloy of selenium and tellurium, or organic photo-semiconductor substances, e.g., polyvinyl carbazoles and arylamines, and a resin binder on a support. The layer may be provided by vacuum deposition. In recent years, a function separated type light-sensitive layer has been widely used in which the function of the photoconductor in the light-sensitive layer is separated; an electric charge-generating agent and an electric charge-transporting agent are used.
The function separated type light-sensitive layer as described above can be divided into two groups; (1) the light-sensitive layer is a single layer containing both the electric charge-generating agent and electric charge-transporting agent; and (2) the light-sensitive layer consists of an electric charge-generating layer containing the electric charge-generating agent and an electric charge-transporting layer containing the electric charge-transporting agent.
These electrophotographic light-sensitive materials, however, suffer from various problems because of poor affinity between the electrically conductive support and the light-sensitive layer; for example, the light-sensitive layer peels apart from the support because of poor adhesion therebetween, and white spots are formed in the formation of images.
In order to overcome the problems as described above, it has been proposed to divide the light-sensitive layer on the electrically conductive support into a photo-conductive layer and an intermediate layer, or to incorporate resins having good adhesive properties into the light-sensitive layer. For this purpose, various resins have been studied and developed. Typical examples are: (1) polyesters (described in, for example, Japanese Patent Application (OPI) No. 68848/82): (2) styrene-butadiene copolymers (described in, for example, Japanese Patent Application (OPI) No. 26739/79); (3) vinylidene chloride-acrylate copolymers (described in, for example, Japanese Patent Publication No. 12864/81); (4) vinyl chloride-vinyl acetate-ethylenic unsaturated acid copolymers (described in, for example, Japanese Patent Application (OPI) No. 47047/81); (5) polyurethane-polyamides (described in, for example, Japanese Patent Application (OPI) No. 114132/76); (6) polyvinyl butyral (described in, for example, Japanese Patent Publication No. 35823/75); (7) polyvinyl alcohol (described in, for example, Japanese Patent Application (OPI) No. 116345/82); and (8) vinylidene chloride-unsaturated monomer-polymerizable ethylenecarboxylic acid copolymers (described in, for example, Japanese Patent Application (OPI) No. 48555/79). The term "OPI" as used herein means a "published unexamined Japanese patent application".
For electrophotographic light-sensitive materials prepared using the resins as described above, the adhesion between the electrically conductive layer and the light-sensitive layer is improved to a certain extent, but other problems arise. For example, the residual potential is high, or although the residual potential is low at first, it is accumulated by repeated use. This causes a decrease in the contrast of images, or the formation of fog. Moreover, some of the electrophotographic light-sensitive materials have poor moisture resistance.
Another problem is that the electric chage retention rate in a diark place is poor.
Still another problem is that when the resins as described above are used in the preparation of an intermediate layer to be provided between the electrically conductive support and the photoconductive layer; in particular, when the photoconductive layer is provided by a coating procedure using organic solvents, the intermediate layer and the photoconductive layer intermingle, causing uneven coating and coating streaks, for example.